Statistics suggest that blood kin are more immune to lethal violence in the United States than non-blood kin. In two U.S. studies genealogical and material relatives were distinguished. In Detroit in 1972, 19 percent of the homicide victims were related to their killers by marriage, as compared with six percent who were related by blood. In Miami in 1980, 10 percent of the homicide victims were marital relatives of their killers, while in 1.8 percent of the homicides the victims were killed by blood relatives. Additionally, in the non-blood relationship of step-child to step-parent, children are more likely to be abused than in a genetic relationship. Male sexual proprietariness is given as a major cause of domestic violence. The researchers also report on evolutionary models related to maternal age in infanticide. Evolutionary psychological constructs should be further tested with less extreme forms of conflict and with positive values of harmony and cooperation. 68 references.